The closed ear inoculates someone against self-improvement. But when the mind’s vault is left open, just a little tweak — what productivity author Charles Duhigg calls a ‘keystone habit’ in his book The Power of Habit: Why We Do What We Do in Life and Business — can lead from one positive change to the next. Take exercise for instance:

“Typically, people who exercise, start eating better and becoming more productive at work. They smoke less and show more patience with colleagues and family. They use their credit cards less frequently and say they feel less stressed. Exercise is a keystone habit that triggers widespread change.”